1. Field of the Invention
The present invention relates generally to a sheet conveying apparatus, more specifically an image forming apparatus provided with a sheet conveying apparatus and to a method of conveying a sheet.
2. Description of the Related Art
In an image forming apparatus, skew and position offset of a recording medium may occur during conveyance of the recording medium. This skew or position offset leads to problems such as conveying jams, poor hand-over to a post-processing apparatus, decreased printing precision, and so forth. Therefore, it is desirable for the image forming apparatus to be provided with some sort of skew correction mechanism.
In Japanese Patent Laid-Open No. 11-208939, a mechanism is proposed whereby skew of a recording medium is detected by two sensors, and skew of the recording medium is corrected by two pairs of skew correction rollers.
Recently, printouts have become more diverse, and so there are increasing demands for printing to a recording medium of a size other than a standard size such as A4. Specifically, with the skew correction mechanism of Japanese Patent Laid-Open No. 11-208939, it is not possible to adequately deal with a recording medium that has been cut into a distinctive shape for design (for example, a cloud form or a star-shape or starburst) other than a rectangle. Here, recording media having such a shape, in other words non-rectangular, will be referred to as irregularly shaped media.
A feature of the skew correction mechanism of Japanese Patent Laid-Open No. 11-208939 is that the skew amount is calculated from the difference between the times at which an arbitrary side of the recording medium passes the two sensors. That is, it is assumed that the recording medium has a shape in which a side is comprised of a straight line, such as a rectangle.
However, irregularly shaped media such as a cloud form or a starburst does not have a clear reference side (e.g. a straight or straight-edged side). Therefore, with the skew correction mechanism of Japanese Patent Laid-Open No. 11-208939, it is not possible to accurately detect the skew amount of irregularly shaped media, and so appropriate skew correction cannot be performed.